All-Iron Redox Flow Battery Tailored for Off-Grid Portable Applications

An all-iron redox flow battery is proposed and developed for end users without access to an electricity grid. The concept is a low-cost battery which the user assembles, discharges, and then disposes of the active materials. The design goals are: (1) minimize upfront cost, (2) maximize discharge energy, and (3) utilize non-toxic and environmentally benign materials. These are different goals than typically considered for electrochemical battery technology, which provides the opportunity for a novel solution. The selected materials are: low-carbon-steel negative electrode, paper separator, porous-carbon-paper positive electrode, and electrolyte solution containing 0.5 m Fe₂(SO₄)₃ active material and 1.2 m NaCl supporting electrolyte. With these materials, an average power density around 20 mW cm⁻² and a maximum energy density of 11.5 Wh L⁻¹ are achieved. A simple cost model indicates the consumable materials cost US$6.45 per kWh⁻¹, or only US$0.034 per mobile phone charge.